A color picture is formed such that electron beams emitted from an electron gun strike phosphors deposited as stripes or dots on the fluorescent layer of a color picture tube. In this process, the conventional method provides that a black matrix is deposited among a color pattern in order to minimize reduction in color purity caused by electron beams' mislanding on corresponding phosphors.
Conventionally, a composition has been used as a composition for use in the black matrix, comprising graphite, surfactant, water and the other additives.
However, the black matrix maded of the above composition does not have the advantage of improving the contrast of the picture, since it cannot filter the internal light, especially a blue light with wave length of 450 nm and a red light with wave length of 620 nm occurring inside when the electron beams strike the phosphors and lowers the contrast.
In order to solve this problem, Japanese specification No. 84-215635 proposes that a blue refractive layer be deposited on blue phosphors and that this layer plays a part in a filter absorbing the internal light of the phosphors. However, this method lowers the color purity, and the complex fabricating process required results in bad productivity.